On any bag or container of fertilizer three numbers will be listed on the front: 20-20-20, 10-30-20, etc. Although these numbers are usually referred to as N-P-K (representing nitrogen, phosphorus and potassium), they actually represent the percentage by weight of these three ingredients. So a 100-pound bag of fertilizer labeled 10-10-10 contains 10 pounds of nitrogen, 10 pounds of phosphate and 10 pounds of potash. The rest of the weight is filler that allows us to spread the fertilizer evenly and to mitigate the possibility of burning the plants with too much fertilizer. See, you probably should have paid better attention in math and chemistry classes.

3. Different plants (and soils) need different formulas.

Many fertilizers are packaged for a specific type of plant, such as roses, azaleas or citrus. Some are formulated to acidify the soil.

Keep in mind: Our soils contain calcium carbonate and are very difficult to acidify. An acid-loving plant should be planted in a container with a potting soil mixture rather than in our native soil.

Also, try not to purchase a fertilizer simply because it says it is for a specific plant without checking the formulation to see if that particular product is what you really need. As with soil mixes, most gardeners have a preferred fertilizer.

4. Fertilizers can be applied many ways.

A dry granular formula such as you might use on lawns can simply be evenly broadcast and watered in. Slow-release formulas - which release nutrients continually over a long period of time - are generally used for container plants and applied as a top dressing.

There are water-soluble powders that are also good for container plants. Foliar sprays are available, too. And, of course, there are organic products to add to the fray. The choices are many and varied, which just adds to the confusion.

Always read the manufacturer's label and follow the application instructions. Many instructions are written as if you were standing in a 10-acre field. Often, the container will have a phone number or website where you can get help in computing the application rate.